UPS Battery, is required to deliver high currents during short discharge times, to ride through short power failures or until standby generator kicks in. To allow the high rate of discharge UPS battery is designed with parallel connected thin plates in order to increase plate's active surface area with the electrolyte.
Charging, is accomplished by connecting battery terminals to a voltage source (charger) with the proper polarity. While charging electrolysis of water decomposes, as a byproduct, water to its ingredients. Oxygen gas is formed at the positive plate and Hydrogen gas at the negative plate.
During discharging the electrochemical energy stored in the electrodes is converted to electrical energy. The electrochemical reactions during discharging, results in water and Lead Sulfate which coats both electrodes, recharging restores the situation.
More information, including electrochemical reaction formulas, see Lead Acid Battery Basics article.
Flooded Lead Acid Battery.
In Flooded, also called Wet , or Conventional Batteries, the oxygen and hydrogen gases formed during charging are vented to the air. They therefore require periodic maintenance, performed by authorized personnel, in order to check the sate of the battery and refill the missing water, if needed. Due to hydrogen’s explosive nature the batteries should be located in separate unmanned and well vented rooms. These are generally used only in large installations, where long life and cost /performance predominate, and where maintenance personnel is available.
In a Sealed Battery, the possibility of gas venting to the air is eliminated. The oxygen diffuses through the separator from the positive plate to the negative plate, where it is recombined with the hydrogen to form water. These batteries do not require water refilling and are therefore called also Maintenance Free batteries.
To enable the possibility of pressure relief, mainly during overcharging, relief valves are installed, to regulate to preset pressure level. Thus, UPS SLA batteries are frequently called Valve Regulated Lead Acid (VRLA) type.
SLA batteries are considered dry type, generally spill proof and leak proof even in case of container cracks or fractures. They can be located within the UPS as any other electrical component.
Following features of the SLA type cause manufactures’ to prefer VRLA technology for Uninterruptible Power Supply applications:
Maintenance free, no water topping up is required during the whole service life.
No equalization charge is normally required.
Non hazardous, have no restrictions for rail, road, sea or air transportation as part
of the system or as separate items.
Rugged and vibration resistant. Can be shipped via parcel post or fast shipping service.
Non corrosive can be used for marine applications or wet environment.
Can be located in any position (horizontal or vertical), enabling design flexibility.
Allow location adjacent to each other or on top of each other (provided that weight and venting are considered). Compact packaging in the enables using internal batteries while increasing capacity and backup time.
About 99% of the gas is recombined within the battery; practically no hydrogen is emitted to the air, can be located in manned locations, where normal venting exists.
The UPS can be designed to allow replacement or hot swapping of failed batteries by the operators, or by local service people.
High rate discharge ability. As requested for systems that provide high energies for relatively short times.
No memory effect. VRLA batteries retain their full charge in float condition during lifetime.
What is a UPS Battery? Operation and Features of Flooded and Maintenance Free VRLA UPS Battery